What does the term anomeric effect refer to?

Answer 1

In organic chemistry, the anomeric effect or Edward-Lemieux effect is a stereoelectronic effect that describes the tendency of heteroatomic substituents adjacent to a heteroatom within a cyclohexane ring to prefer the axial orientation instead of the less hindered equatorial orientation that would be expected from steric considerations.

This effect was originally observed in pyranose rings by J. T. Edward in 1955; at that time, N.-J. Chii and R. U. Lemieux began to study the anomerization equilibria of the fully acetylated derivatives of several aldohexopyranoses. The term "anomeric effect" was introduced in 1958.

The anomeric effect received its name from the term used to designate the C-1 carbon of a pyranose, the anomeric carbon. Isomers that differ only in the configuration at the anomeric carbon are called anomers.

Answer 2

The anomeric effect is a stereoelectronic effect where the lone pair of electrons on the heteroatom in a cyclic hemiacetal or hemiketal interacts with the adjacent sigma* antibonding orbital, leading to the stabilization of the axial or equatorial orientation of the anomeric carbon. This effect influences the conformation and reactivity of carbohydrates and other compounds with similar functional groups.